1. Field of the Invention
The present invention relates to an elastic roller for fixing electrophotographic images, and more specifically, to an image fixing elastic roller which is used as a pressure roller for uniformly pressing an image support sheet relative to an image fixing heating roller.
2. Description of the Prior Art
In general, fixing devices of conventional electrophotographic copying machines or the like are structured such that a non-fixed toner image transferred onto an image support sheet, such as a paper sheet, is heat-pressed between a non-adhesive heating roller and an elastic pressure roller so as to be melted and fixed thereon.
Conventional toner image fixing devices are generally, formed by providing a heat-resisting elastic layer, such as silicone sponge, around a metal core, and further providing a non-adhesive layer, such as a fluoroplastic, on the outer periphery of the elastic layer to prevent the adhesion of toner to the pressure roller.
Since it is common to operate such a fixing device intermittently, it is desired that the heating roller rapidly increases its surface temperature to start the fixing operation within a short period of time after the fixing device is brought into operation. Similarly, it is also desired that the pressure roller approaches the surface temperature of the heating roller within a short period of time after the fixing device is brought into operation. In view of this, the elastic layer of the pressure roller is generally formed of a sponge layer having a relatively low heat capacity and low heat conductivity.
However, there has been a problem such that it has been difficult to fix high-quality images on a number of paper sheets continuously in accordance with the prior art fixing devices, since paper wrinkles are easily formed with a lapse of operating time after the activation of the fixing device.